The present invention relates to a method and apparatus for operating a machine that detects a state of an element of the machine for controlling operation of the machine.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Machines in which a controller connects a drive to a power supply via at least one actuator and receives a time-dependent signal from a sensor in the machine are generally known. Typical examples of such machines are drilling machines, lathes, circular saws and band saws as well as other machines. In many cases, the drive is a rotating drive. In some cases, however, the drive may be in the form of a linear drive.
Machines generally have many individual components. Some of the components are rigid, while others are movable but are usually not moved and yet others are moved in the normal state. Examples of rigid components are the basic body of the machine and the lining of the machine. One example of a component which is rarely moved is a covering shroud which is used to cover a machining area of the machine. Movable parts are, for example, shafts, bearings and spindles. The individual components of the machine are subject to wear and other changes over time. Some of these changes are harmless, some are critical, and some require immediate intervention in the operating sequence in order to avoid consequential damage.
It is known practice to provide sensors in order to monitor critical components. For example, temperature sensors are arranged in the vicinity of rolling bearings in order to be able to detect rolling bearing damage as early as possible. The use of acceleration sensors, distance sensors or pressure sensors is also known. The sensor signals determined by the sensor used, in particular the temporal change in said signals, and predefined limit values make it possible, in many cases, to draw conclusions on the state of rolling bearings or other components of the machine.
The procedure in the prior art has various disadvantages. For example, the sensors used and, in particular, the evaluation circuits used are often expensive. Furthermore, it is often difficult to integrate the sensors and the evaluation circuits in the machine or in the electrical drive. Furthermore, the sensors are often susceptible to interference. It is often also difficult to transmit signals. Furthermore, in many cases, a single signal does not suffice to clearly and reliably describe the system state. Furthermore, the practice of coupling external sensor signals or signals from evaluation circuits into a numerical controller or into a converter is associated with a considerable amount of effort in many cases and is also undesirable for technical reasons attributable to the system. Furthermore, interference and other process influences during operation often prevent the detected signals from being clearly evaluated. Finally, meaningful and convincing limit values for determining wear states cannot always be determined reliably since the individual components of the machine interact with one another.
It would therefore be desirable and advantageous to address prior art problems and to obviate other prior art shortcomings and to determine the state of rolling bearings and other components of the machine in a cost-effective, simple and clear manner.